I found two interesting feats and wanted to know if they stack:
Splintering Weapon
Whenever you use a melee or thrown weapon with the fragile weapon feature or similar quality and hit an opponent, you can give your weapon the broken condition to deal that opponent 1d4 points of bleed damage.
Chairbreaker
When you attack a target with an improvised weapon, you can give that weapon the broken condition to deal 1d4 points of additional damage on that attack.
Additionally, you gain a +4 bonus on the roll to confirm a critical hit with this attack. If you confirm the crit, the extra damage granted by this feat is also multiplied and the improvised weapon is destroyed.
From what I understand it seems like it could stack, because the broken condition means it has lost half its hit points. So during an attack could I apply the broken property twice (thus destroying the weapon) to apply an extra 2d4 damage?
A) I don't think you can apply the broken condition twice. Once your weapon is broken, it's broken, and it doesn't become more broken until it's destroyed. There's no clause in the description of the broken condition that states anything about applying the broken condition a second time to become destroyed.
B) Even if you could, stacking Splintering with Chairbreaker gets you 1d4 bleed (applied on the TARGET's turn before anything else happens) and 1d4 additional damage on the hit. That's subtly different that an extra 2d4 damage.